The invention concerns a transfer case for motor vehicles with off-the-road gear, comprising a casing, an input shaft, a first output shaft, coaxial with the latter, a second output shaft, offset therefrom, a speed-reduction unit, a coupling unit and an offset drive. This form of transfer case is also referred to as “single-offset”. It is used in particular for fourwheel-drive passenger motor vehicles and light commercial vehicles with longitudinal engine-transmission assembly, it being possible to change over from the on-the-road gear into an off-the-road gear by means of the speed-reduction unit, often dispensing with an interaxle differential and it being possible to cut in the drive of the second driven axle.
A transfer case of the generic type is known from EP 882 912 A2. In this transfer case, the speed-reduction unit is, on the side of the input shaft, a planetary transmission with an internal-geared wheel fixed to the casing and an output on the planet carrier. Right behind it is the associated shifting device. This is then followed by the driving wheel of the offset drive and, finally, a coupling for the cutting-in of the second driven axle.
This arrangement has various disadvantages. Because of the internal-geared wheel fixed to the casing, the planetary transmission also continues to run in meshing engagement in the on-the-road gear, which increases the noise generated and the amount of wear; moreover, when designing planetary transmissions of this type, planetary wheels that are unfavorably small for the reduction ratios customary for an off-the-road gear are obtained. Furthermore, internal-geared wheels are relatively expensive to produce. The shifting device between the planetary transmission and the driving wheel of the offset drive increases the overall length and displaces the offset drive to the rear, both being unfavorable for various reasons including the emission of structure-borne sound through the casing.
It is therefore the object of the invention to overcome the drawbacks mentioned of a transfer case of the generic type. It is intended to run quietly and with little wear, be as small and inexpensive as possible, and the second output shaft is to be as far forward as possible.